Databases Reference
In-Depth Information
MV Terminology
A great many terms relate to refreshing MVs. You should be familiar with these terms before delving into how to
implement the features. Table
15-1
defines the various terms relevant to MVs.
Table 15-1.
MV Terminology
Term
Meaning
Materialized view (MV)
Database object used for replicating data and improving query performance
MV SQL statement
SQL query that defines what data are stored in the underlying MV base table
MV underlying table
Database table that has the same name as the MV and that stores the result of the MV
SQL query
Table that an MV references in its
FROM
clause of the MV SQL statement
Master (base) table
Complete refresh
Process in which an MV is deleted from and completely refreshed with an MV SQL
statement
Fast refresh
Process during which only DML changes (against base table) that have occurred
since the last refresh are applied to an MV
MV log
Database object that tracks DML changes to the MV base table. An MV log is required
for fast refreshes. It can be based on the primary key,
ROWID
, or object ID.
Simple MV
MV based on a simple query that can be fast refreshed
Complex MV
MV based on a complex query that isn't eligible for fast refresh
Build mode
Mode that specifies whether the MV should be immediately populated or deferred
Refresh mode
Mode that specifies whether the MV should be refreshed on demand, on commit,
or never
Refresh method
Option that specifies whether the MV refresh should be complete or fast
Query rewrite
Feature that allows the optimizer to choose to use MVs (instead of base tables) to
fulfill the requirements of a query (even though the query doesn't directly reference
the MVs)
Local MV
MV that resides in the same database as the base table(s)
Remote MV
MV that resides in a database separate from that of the base table(s)
Refresh group
Set of MVs refreshed at the same consistent transactional point
Refer back to Table
15-1
as you read the rest of this chapter. These terms and concepts are explained and
expounded on in subsequent sections.
Referencing Useful Views
When you're working with MVs, sometimes it's hard to remember which data dictionary view to query under a
particular circumstance. A wide variety of data dictionary views are available. Table
15-2
contains a description
of the MV-related data dictionary views. Examples of using these views are shown throughout this chapter where
appropriate. These views are invaluable for troubleshooting, diagnosing issues, and understanding your MV
environment.
